Method for making carbon nanotube arrays

ABSTRACT

A method for making a carbon nanotube array includes placing a gas diffusing unit defining an outlet in a chamber including a first inlet and a second inlet. A gas transporting pipe haves a first end and a second end opposite to the first end, the second end is connected to the gas diffusing unit, and the first end passes through the second inlet and extends out of the chamber. A growth substrate defining a through hole covers the outlet. A carbon source gas and a protective gas is supplied to the chamber from the first inlet, to grow a carbon nanotube array including multiple carbon nanotubes. Each carbon nanotube has a bottom end. Then the carbon source gas is stopped supplying, and an oxygen containing gas is supplied to the gas transporting pipe, to oxidize the bottom end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Pat. No.10,787,364, filed on Oct. 10, 2018, entitled, “DEVICE FOR MAKING CARBONNANOTUBE ARRAYS”, which claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201810764482.6, filed on Jul. 12,2018, in the China National Intellectual Property Administration, thedisclosure of which is incorporated herein by reference.

FIELD

The present application relates to a method for making carbon nanotubearrays.

BACKGROUND

Carbon nanotubes can be composed of a number of coaxial cylinders ofgraphite sheets, and have recently attracted a great deal of attentionfor use in different applications, such as field emitters, chemicalsensors, and so on. Carbon nanotubes can be prepared by Chemical VaporDeposition (CVD), Arc Discharge, or Laser Ablation. When growing carbonnanotube arrays on a growth substrate by the CVD method, the carbonnanotube arrays adhere to the growth substrate and it can be difficultto separate the carbon nanotube array from the growth substrate.Furthermore, it can be difficult to obtain an integrated carbon nanotubearray by peeling the carbon nanotube array from the growth substrateusing a knife or a tweezer, because the bonding force between the carbonnanotubes and the growth substrate is strong.

Therefore, there is room for improvement in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 is a schematic of a first embodiment of a device for making acarbon nanotube array.

FIG. 2 is a schematic of the first embodiment of a gas diffusing unit.

FIG. 3 is a schematic of the first embodiment of a growth substrate.

FIG. 4 is a schematic of the first embodiment of another growthsubstrate.

FIG. 5 is a schematic of the first embodiment of a composite structureformed by a gas transporting pipe, the gas diffusing unit, and thegrowth substrate.

FIG. 6 is a process flow of a method for making the carbon nanotubearray using the device of FIG. 1.

FIG. 7 is a schematic of a second embodiment of a composite structureformed by the gas transporting pipe, a gas diffusing unit, and thegrowth substrate.

FIG. 8 is a schematic of a third embodiment of a composite structureformed by the gas transporting pipe, a gas diffusing unit, and thegrowth substrate.

FIG. 9 is a schematic of a fourth embodiment of a composite structureformed by the gas transporting pipe, a gas diffusing unit, and thegrowth substrate.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated to illustratedetails and features better. The description is not to be considered aslimiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The term “substantially” is defined to be essentially conforming to theparticular dimension, shape, or another word that substantiallymodifies, such that the component need not be exact. For example,substantially cylindrical means that the object resembles a cylinder,but can have one or more deviations from a true cylinder. The term“comprising” means “including, but not necessarily limited to”; itspecifically indicates open-ended inclusion or membership in aso-described combination, group, series, and the like.

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

FIG. 1 and FIG. 5 show a device 10 for making a carbon nanotube array ina first embodiment and that includes a chamber 12, a gas transportingpipe 14, a gas diffusing unit 16, and a heater 18. The gas transportingpipe 14 and the gas diffusing unit 16 are located in the chamber 12.

The chamber 12 has a first sidewall 122 and a second sidewall 124opposite to the first sidewall 122. The first sidewall 122 defines afirst inlet 1222 and a second inlet 1224 spaced apart from the firstinlet 1222, and the second sidewall 124 defines a first outlet 1242. Thecarbon source gas and the protective gas enter the chamber 12 from thefirst inlet 1222, and gas generated by various reactions in the chamber12 can be exhausted from the first outlet 1242. The chamber 12 can beformed by a material with stable chemical properties andhigh-temperature resistance. In one embodiment, the chamber 12 is aquartz tube. A flowmeter can be installed in the chamber 12 to detectthe gas flow, or a pressure sensor, such as a piezometer, can beinstalled in the chamber 12 to detect the pressure of the chamber 12.The chamber 12 can be connected to a vacuum pump to reduce the pressurein the chamber 12.

The gas transporting pipe 14 transports gas to the gas diffusing unit16. The gas transporting pipe 14 has a first end 142 and a second end144 opposite to the first end 142, the second end 144 is incommunication with the chamber 12 and connected to the gas diffusingunit 16, and the first end 142 passes through the second inlet 1224 andextends out of the chamber 12, communicating with the outside of thechamber 12. The gas transporting pipe 14 is hermetically connected tothe gas diffusing unit 16. The connection manner between the gastransporting pipe 14 and the gas diffusing unit 16 is not limited, aslong as gas can be supplied or diffused from the gas transporting pipe14 to the gas diffusing unit 16. The gas transporting pipe 14 can beintegrated with the gas diffusing unit 16. The gas transporting pipe 14can also be detachably connected to the gas diffusing unit 16.

The gas diffusing unit 16 diffuses the gas into the chamber 12 andsupports a growth substrate 13 for growing carbon nanotube arrays. FIG.2 and FIG. 5 show the gas diffusing unit 16 is a hollow structure andincludes a bottom wall 162 and a sidewall 164. The sidewall 164 definesa first through hole 166, and the second end 144 of the gas transportingpipe 14 passes through the first through hole 166, so that the gastransporting pipe 14 inserts into the gas diffusing unit 16. The gasdiffusing unit 16 defines a space 168 and a second outlet 167, and thesecond outlet 167 is opposite to the bottom wall 162. The sidewall 164and the bottom wall 162 define the space 168. The sidewall 164 can becubic, circular, or a trapezoidal. Thus, the shape of the gas diffusingunit 16 is not limited, such as cubic, circular, or trapezoidal. In oneembodiment, the shape of the gas diffusing unit 16 is cubic. As shown inFIG. 2, the sidewall 164 includes a first sidewall 1642, a secondsidewall 1644 opposite to the first sidewall 1642, a third sidewall1646, and a fourth sidewall 1648 opposite to the third sidewall 1646.The first sidewall 1642 defines the first through hole 166, and the gastransporting pipe 14 inserted into the first through hole 166. Thebottom wall 162, the first sidewall 1642, the second sidewall 1644, thethird sidewall 1646, and the fourth sidewall 1648 encircle the space168. The gas enters the gas transporting pipe 14 from the first end 142,passes through the gas transporting pipe 14 to enter the gas diffusingunit 16, and finally passes through the second outlet 167 to enter thechamber 12. The gas diffusing unit 16 can be a semi-closed container. Inone embodiment, the gas diffusing unit 16 is a quartz boat.

The growth substrate 13 that grows carbon nanotube arrays has a firstgrowth substrate surface 132 and a second growth substrate surface 134opposite to the first growth substrate surface 132. The growth substrate13 defines a plurality of spaced-apart second through holes 136. Thesecond through holes 136 passes through the growth substrate 13 alongthe thickness direction of the growth substrate 13, and each secondthrough hole 136 extends from the first growth substrate surface 132 tothe second growth substrate surface 134, as shown in FIG. 5. The shapeof each second through hole 136 is not limited, such as circle, square,triangle, diamond, or rectangle. The shapes of the second through holes136 can be different from each other. When the second through hole 136is circular, as shown in FIG. 3, the diameter of the circular throughhole is in a range from about 10 nanometers to about 1 centimeter. Whenthe second through hole 136 is a strip through hole, as shown in FIG. 4,the width of the strip through hole is in a range from about 10nanometers to about 1 centimeter.

The growth substrate 13 is resistant to high temperatures, does notreact with the carbon source gas and the protective gas, and does notundergo atomic permeation. The material of the growth substrate 13 canbe silicon, quartz, or the like. In one embodiment, the growth substrate13 is a silicon wafer. A protective layer is formed on the siliconwafer, for example, the protective layer is a silicon oxide layer, andthe thickness of the silicon oxide layer ranges from about 1 nanometerto about 1000 nanometers. The first growth substrate surface 132 can betreated by mechanical polishing or electrochemical polishing, to ensurethe smoothness of the first growth substrate surface 132 meets the needsof growing carbon nanotube arrays.

FIG. 5 shows the growth substrate 13 is suspended on the gas diffusingunit 16 and covers the second outlet 167. The method for placing thegrowth substrate 13 on the sidewall 164 of the gas diffusing unit 16 isnot limited. In one embodiment, the size of the growth substrate 13 isgreater than the size of the second outlet 167, such that the growthsubstrate 13 is directly placed on the sidewall 164 and covers thesecond outlet 167. The gas in the gas diffusing unit 16 can pass throughthe second outlet 167 and the second through holes 136 to enter theinside of the chamber 12.

The heater 18 heats the growth substrate 13. The heater 18 is locatedinside of the chamber 12 or located outside of the chamber 12. Theheater 18 can be formed by carbon nanotubes or electrothermal resistancewires surrounding the periphery of the chamber 12 to heat the inside ofthe chamber 12, so that the growth substrate 13 is heated. In otherembodiments, the heater 18 can also be a high-frequency furnace or alaser heater, that only heats the growth substrate 13. For example, theheater 18 is disposed above or below the gas diffusing unit 16, only toheat the growth substrate 13 without heating the entire chamber 12,thereby saving energy.

FIG. 6 shows a method for making the carbon nanotube array by the device10 of FIG. 1. Depending on the embodiment, certain of the steps orblocks described may be removed, others may be added, and the sequenceof steps or blocks may be altered. It is also to be understood that thedescription and the claims drawn to a method may include some referencenumeral indication referring to certain blocks or steps. However, thereference numeral indication used is only for identification purposesand not interpreted as a suggestion as to an order for the steps. Themethod includes one or more of the following steps:

-   -   S1, providing the growth substrate 13 having the first growth        substrate surface 132 and the second growth substrate surface        134 opposite to the first growth substrate surface 132, wherein        the growth substrate 13 defines the second through holes 136,        and the second through holes 136 extend from the first growth        substrate surface 132 to the second growth substrate surface        134;    -   S2, depositing a catalyst layer 15 on the first growth substrate        surface 132;    -   S3, placing the gas diffusing unit 16 in the chamber 12, wherein        the chamber 12 includes the first inlet 1222 and the second        inlet 1224 spaced apart from each other, the gas diffusing unit        16 is a hollow structure and defines the space 168, the second        outlet 167 and the first through hole 166;    -   S4, providing the gas transporting pipe 14 having a first end        142 and a second end 144 opposite to the first end 142, wherein        the second end 144 is in the chamber 12 and connected to the gas        diffusing unit 16, and the first end 142 passes through the        second inlet 1224 and extends out of the chamber 12;    -   S5, placing the growth substrate 13 on the gas diffusing unit 16        and cover the second outlet 167, wherein the growth substrate 13        is located between the catalyst layer 15 and the gas diffusing        unit 16;    -   S6, supplying the carbon source gas and the protective gas to        the chamber 12 from the first inlet 1222, and heating the growth        substrate 13 to a first temperature, to grow the carbon nanotube        array on the first growth substrate surface 132, wherein the        carbon nanotube array includes a plurality of carbon nanotubes,        and each of the plurality of carbon nanotubes has a bottom end;        and    -   S7, stopping supplying the carbon source gas to the chamber 12,        supplying an oxygen containing gas to the gas transporting pipe        14 from the first end 142 and heating the carbon nanotube array        to a second temperature, to oxidize the bottom end of each of        the plurality of carbon nanotubes.

During step S2, the thickness of the catalyst layer 15 ranges from about1 nanometer to about 10 nanometers. In one embodiment, the thickness ofthe catalyst layer 15 ranges from about 1 nanometer to about 5nanometers. The catalyst layer 15 can be formed on the first growthsubstrate surface 132 by evaporation, sputtering, or chemicaldeposition. The material of the catalyst layer 15 can be iron, cobalt,nickel, or an alloy of any combination thereof. The catalyst layer 15can further be annealed, the annealing under air atmosphere temperatureranges from about 200 degrees Celsius to about 400 degrees Celsius, andthe annealing time ranges from about 8 hours to about 12 hours. Afterannealing the catalyst layer 15 under an air atmosphere, the catalystlayer 15 can be oxidized to form metal oxide, and the catalyst layer 15can become uniformly distributed metal oxide catalyst nanoparticles. Thecatalytic activity of the catalyst nanoparticles is better than thecatalytic activity of the continuous catalyst layer 15. In oneembodiment, the material of the catalyst layer 15 is iron, the thicknessof the iron catalyst layer 15 is about 2 nanometers, and the ironcatalyst layer 15 is annealed at 300 degrees Celsius for 10 hours underthe air atmosphere.

When the growth substrate 13 is a silicon substrate, the metal of thecatalyst layer 15 deposited on the first growth substrate surface 132may react with the silicon of the first growth substrate surface 132 toform an alloy, and this alloy would affect the activity of the catalystlayer 15. Thus, before the catalyst layer 15 is deposited on the firstgrowth substrate surface 132 of the silicon substrate, a catalystcarrier layer can be formed on the first growth substrate surface 132.Thus, the metal of the catalyst layer 15 cannot react with the firstgrowth substrate surface 132, and the activity of the catalyst layer 15would not be affected. The material of the catalyst carrier layer can bealuminum (Al), aluminum oxide (Al₂O₃), silicon oxide (SiO₂), ormagnesium oxide (MgO). The thickness of the catalyst carrier layerranges from about 1 nanometer to about 10 nanometers. In one embodiment,the catalyst carrier layer is an aluminum layer, and the thickness ofthe aluminum layer ranges from about 3 nanometers to about 7 nanometers.It is understood that the catalyst layer 15 and the catalyst carrierlayer do not cover each second through hole 136. The oxygen containinggas can still enter the chamber 12 by passing through the second throughholes 136 after forming the catalyst layer 15 and the catalyst carrierlayer.

During step S5, the growth substrate 13 is suspended on the secondoutlet 167 of the gas diffusing unit 16 and covers the second outlet167. The first growth substrate surface 132 of the growth substrate 13is away from the gas diffusing unit 16, some portions of the secondgrowth substrate surface 134 of the growth substrate 13 is in directcontact with the sidewall 164 of the gas diffusing unit 16.

During step S6, the protective gas is an inert gas or nitrogen. Thecarbon source gas is a hydrocarbon compound, such as acetylene,ethylene, methane, ethane, or the like. The first temperature is thegrowth temperature of the carbon nanotube array. The first temperatureranges from 600 degrees Celsius to 720 degrees Celsius. In oneembodiment, the first temperature ranges from 620 degrees Celsius to 700degrees Celsius. The growth substrate 13 is heated to the firsttemperature under a protective gas atmosphere, and then the carbonsource gas and the protective gas mixture is supplied into the chamber12, so that the carbon nanotube array is grown on the first growthsubstrate surface 132 by chemical vapor deposition. The time forsupplying the carbon source gas and the protective gas mixture rangesfrom about 10 minutes to about 40 minutes. During growing carbonnanotube arrays on the first growth substrate surface 132, the pressurein the chamber 12 ranges from about 2 torrs to 8 torrs.

The carbon source gas, such as acetylene, direct contacts the catalystlayer 15 and pyrolyzed into carbon units (—C═C— or C) and hydrogen (H₂)due to the catalysis of the catalyst layer 15. When the hydrogendiffuses to the surface of the metal oxide catalyst nanoparticles, themetal oxide catalyst nanoparticles can be reduced to metal catalystnanoparticles. Thus, the oxidized catalyst can be reduced and activated.Then, the carbon units are adsorbed on the surface of catalyst layer 15,thereby growing carbon nanotube arrays on the first growth substratesurface 132. In one embodiment, the protective gas is nitrogen, thecarbon source gas is acetylene, the first temperature is about 700degrees Celsius, and the pressure of the chamber 12 is about 5 torrs.

Each carbon nanotube includes a top end, the bottom end, and a middleportion between the top end and the bottom end. The bottom end is indirect contact with the first growth substrate surface 132, and themiddle portion and the top end are away from the first growth substratesurface 132.

During step S7, stopping supplying the carbon source gas to the chamber12, continuously supplying the protective gas to chamber 12 from thefirst inlet 1222 and supplying the oxygen containing gas to the gastransporting pipe 14 from the first end 142. Alternatively, stoppingsupplying the carbon source gas to the chamber 12, and supplying theoxygen containing gas and the protective gas to the gas transportingpipe 14 from the first end 142. The oxygen containing gas passes throughthe gas transporting pipe 14, the gas diffusing unit 16, and the secondthrough holes 136 of the growth substrate 13 to reach the first growthsubstrate surface 132, so the bottom ends of the carbon nanotubes areoxidized at the second temperature. The oxygen containing gas can bepure oxygen or air. The flow rate of oxygen containing gas ranges fromabout 300 standard millimeters per minute (sccm) to 500 sccm. Thetemperature of the growth substrate 13 is changed to be the secondtemperature, the second temperature is the temperature of oxidizing thebottom ends of the carbon nanotubes, and the second temperature can bein a range from about 500 degrees Celsius to about 800 degrees Celsius.The time for oxidizing the bottom ends of the carbon nanotubes by theoxygen containing gas is defined as an oxidizing time, and the oxidizingtime is in a range from about 5 minutes to about 20 minutes. Duringoxidizing the bottom ends of the carbon nanotubes, the pressure in thechamber 12 is still in a range from about 2 torrs to about 8 torrs. Inone embodiment, the pressure in the chamber 12 is about 5 torrs. Theflow rate of oxygen containing gas, the oxidizing time, and the pressurein the chamber 12 can ensure that only bottom ends of the carbonnanotubes are oxidized.

After the bottom ends of the carbon nanotubes are oxidized, the supplyof oxygen containing gas is stopped, but the supplying of the protectivegas from the first inlet 1222 or the second inlet 1224 continues. Afterthe temperatures of the oxidized carbon nanotube array and growthsubstrate 13 naturally fall below 400 degrees Celsius, the growthsubstrate 13 and the oxidized carbon nanotube array are slowly taken outof the chamber 12.

In one embodiment, the second temperature is 700 degrees Celsius, theflow rate of the oxygen containing gas is 500 sccm, and the oxidizingtime ranges from about 9 minutes to about 10 minutes. In one embodiment,the second temperature is 800 degrees Celsius, the flow rate of theoxygen containing gas is 300 sccm, and the oxidizing time ranges fromabout 5 minutes to about 7 minutes. In one embodiment, the secondtemperature is 500 degrees Celsius, the flow rate of the oxygencontaining gas is 500 sccm, and the oxidizing time ranges from about 16minutes to about 20 minutes. In one embodiment, the oxygen containinggas is supplied in the process of naturally reducing the temperatures ofthe growth substrate 13, the flow rate of the oxygen containing gas is500 sccm, and the oxidizing time ranges from about 13 minutes to about15 minutes.

The second temperature, the oxidizing time, and the flow rate of theoxygen containing gas are related to the quality of the carbon nanotubearray. When the quality of the carbon nanotube array is low, forexample, the carbon nanotube array contains many defects and amorphouscarbons, the second temperature can be appropriately decreased, theoxidizing time can be shortened, and the flow rate of the oxygencontaining gas can be decreased. When the quality of the carbon nanotubearray is high, for example, the carbon nanotube array substantially hasno impurity, the second temperature can be appropriately increased, theoxidizing time can be prolonged, and the flow rate of the oxygencontaining gas can be increased.

It can be understood that when the second temperature and the flow rateof the oxygen containing gas are constant, the oxidizing time cannot betoo long or too short. When the oxidizing time is too long, the carbonnanotube array is can be seriously damaged and the height of the carbonnanotube array will be greatly reduced. When the oxidizing time is tooshort, separating the oxidized carbon nanotube array from the growthsubstrate 13 can be difficult.

After step S7, a step of separating the oxidized carbon nanotube arrayfrom the growth substrate 13 is further included. After the bottom endsof the carbon nanotubes are oxidized, the oxidized carbon nanotube arrayis separated from the growth substrate 13 just by applying an externalforce, such as, just lightly shaking the growth substrate 13, justblowing on the oxidized carbon nanotube array, just tilting the growthsubstrate 13, or just reversing the growth substrate 13. In oneembodiment, after the bottom ends of the carbon nanotubes are oxidized,the oxidized carbon nanotube array is separated from the growthsubstrate 13 just by blowing on the oxidized carbon nanotube array bymouth. When the growth substrate 13 is tilted, an extending direction ofthe growth substrate 13 and a horizontal plane form an angle, and theangle is larger than or equal to 30 degrees. In one embodiment, theangle is equal to about 90 degrees. When the growth substrate 13 istilted or reversed, the oxidized carbon nanotube array falls only bygravity. Alternatively, the oxidized carbon nanotube array is moreeasily peeled from the growth substrate 13 using a knife or a tweezerthan the non-oxidized carbon nanotube array. Furthermore, when thegrowth substrate 13 and the oxidized carbon nanotube array are taken outof the chamber 12, taking the growth substrate 13 and the oxidizedcarbon nanotube array out of the chamber 12 cannot be too fast, and thespeed of taking the growth substrate 13 and the oxidized carbon nanotubearray out of the chamber 12 is greater than 0 cm/min and less than 100cm/min. When the speed of taking the growth substrate 13 and theoxidized carbon nanotube array out of the chamber 12 is greater than orequal to 100 cm/min, the oxidized carbon nanotube array can fall off thegrowth substrate 13.

In the process of growing carbon nanotube arrays, for each carbonnanotube, first the top end grows, then the middle portion grows, andfinally the bottom end grows. At the later growth stage of the carbonnanotube array, the catalytic activity of the catalyst layer 15decreases, resulting in the bottom end having more defects than the topend and the middle portion. When the oxygen containing gas is suppliedto the carbon nanotube array, the oxygen containing gas can contact thetop end, the bottom end, and the middle portion of each carbon nanotube.However, it is easier for the oxygen containing gas to react with thebottom end than to react with the top end and the middle portion,because the bottom end has more defects than the top end and the middleportion. The reaction between the oxygen containing gas and the bottomend produces carbon dioxide and weakens the bonding force between eachcarbon nanotube and the first growth substrate surface 132 of the growthsubstrate 13. The middle portion and the top end of each carbon nanotubeonly have a few defects, thus it is not easy for the middle portion andthe top end to react with the oxygen containing gas, thereby keeping theintegrity of the carbon nanotube array. Thus, the top end and the middleportion of each carbon nanotube are not oxidized, and the bottom end ofeach carbon nanotube is oxidized.

The bottom end of each carbon nanotube is oxidized, to weaken thebonding force between the bottom end of each carbon nanotube and thefirst growth substrate surface 132 allowing for easy separation usingthe methods described above. Thus, the structure of the carbon nanotubearray cannot be destroyed, and an integrated carbon nanotube array canbe obtained. Additionally, when the bottom end of each carbon nanotubeis separated from the growth substrate 13, the catalyst layer 15 remainson the first growth substrate surface 132 of the growth substrate 13.The carbon nanotube array contains a few catalyst metal particles ordoes not contain the catalyst metal particles after being separated fromthe growth substrate 13, thereby improving the quality or the purity ofthe carbon nanotube array.

The original carbon nanotube array growing on the first growth substratesurface 132 and the oxidized carbon nanotube array are the same exceptfor their bottom ends. The bottom ends of the original carbon nanotubearray are not oxidized. When only bottom ends of the original carbonnanotube array are oxidized, the oxidized carbon nanotube array isformed. Furthermore, the original carbon nanotube array is afree-standing structure. The term “free-standing” includes, but notlimited to, the original carbon nanotube array that does not have to besupported by a substrate. For example, the free-standing carbon nanotubearray can sustain the weight of itself when it is hoisted by a portionthereof without any significant damage to its structural integrity. So,if the free-standing carbon nanotube array is placed between twoseparate supporters, a portion of the free-standing carbon nanotubearray, not in contact with the two supporters, would be suspendedbetween the two supporters and yet maintain film structural integrity.The oxidized carbon nanotube array is also a free-standing structure.The oxidized carbon nanotube array separated from the growth substrate13 is still a free-standing structure.

The oxygen containing gas enters the gas transporting pipe 14 from thefirst end 142 and passes through the gas transporting pipe 14, the gasdiffusing unit 16, and the second through holes 136 of the growthsubstrate 13, to enter the chamber 12. In the process of supplying theoxygen containing gas to the chamber 12, the oxygen containing gas canonly contact with and oxidize the bottom end of each carbon nanotube bycontrolling the time for supplying the oxygen containing gas to thechamber 12. For example, after oxidizing the bottom end of each carbonnanotube, the supplying of the oxygen containing gas is stopped. Thus,the chances that the middle portion and top end of each carbon nanotubewill react with the oxygen containing gas can be reduced, reducing theloss of the carbon nanotube array and improving the integrity of thecarbon nanotube array.

FIG. 7 shows a gas diffusing unit 26 of a second embodiment. The gasdiffusing unit 26 is similar to the gas diffusing unit 16 of the firstembodiment above except that each of at least the first sidewall 1642and the second sidewall 1644 has a step. The step is in the space 168and used for supporting the growth substrate 13. The step is adjacent toone end of each of the first sidewall 1642 and the second sidewall 1644.The growth substrate 13 can be located on and fixed by the steps of thefirst sidewall 1642 and the second sidewall 1644.

In the second embodiment, the method for separating the oxidized carbonnanotube array from the growth substrate 13 is provided. The method forseparating the oxidized carbon nanotube array from the growth substrate13 in the second embodiment is similar to the method for separating theoxidized carbon nanotube array from the growth substrate 13 in the firstembodiment.

FIG. 8 shows a gas diffusing unit 36 of a third embodiment The gasdiffusing unit 36 is similar to the gas diffusing unit 26 of the secondembodiment above except that each of at least the first sidewall 1642and the second sidewall 1644 has a plurality of steps. The plurality ofsteps are in the space 168 and can be used for supporting a plurality ofgrowth substrates 13 with different sizes, thereby meeting differentproduction needs.

In the third embodiment, the method for separating the oxidized carbonnanotube array from the growth substrate 13 is provided. The method forseparating the oxidized carbon nanotube array from the growth substrate13 in the third embodiment is similar to the method for separating theoxidized carbon nanotube array from the growth substrate 13 in the firstembodiment.

FIG. 9 shows a gas diffusing unit 46 of a fourth embodiment. The gasdiffusing unit 46 is similar to the gas diffusing unit 16 of the firstembodiment above except that the gas diffusing unit 46 further includesa plate 161 covering the second outlet 167, and the plate 161 has aplurality of third through holes 1612 spaced from each other. The plate161 supports the growth substrate 13. The material of the plate 161 isnot limited. In one embodiment, the plate 161 is a quartz mesh, and theplurality of third through holes 1612 corresponds to the second throughholes 136 of the growth substrate 13 one to one. The gas in the gasdiffusing unit 16 can enter inside of the chamber 12 by passing throughthe plurality of third through holes 1612 and the second through holes136.

In the fourth embodiment, the method for separating the oxidized carbonnanotube array from the growth substrate 13 is provided. The method forseparating the oxidized carbon nanotube array from the growth substrate13 in the fourth embodiment is similar to the method for separating theoxidized carbon nanotube array from the growth substrate 13 in the firstembodiment.

The devices and the method above for making the carbon nanotube arrayhave the following advantages: the chamber 12 defines the first inlet1222 and the second inlet 1224 spaced from each other, and the first end142 of the gas transporting pipe 14 passes through the second inlet 1224to extend out of the chamber 12; the carbon source gas and theprotective gas are supplied to the chamber 12 from the first inlet 1222,to grow the carbon nanotube array on the first growth substrate surface132 of the growth substrate 13; and after growing carbon nanotube arraysis finished, the oxygen containing gas and the protective gas mixture oronly the oxygen containing gas enters the chamber 12 from the first end142 of the gas transporting pipe 14, to oxidize the bottom ends of thecarbon nanotubes. Thus, the bonding force between each carbon nanotubeand the first growth substrate surface 132 of the growth substrate 13 isweakened, thus an integrated carbon nanotube array can be separated fromthe growth substrate 13.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Additionally, it is also to be understood that the above description andthe claims drawn to a method may comprise some indication in referenceto certain steps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A method for making a carbon nanotube array, themethod comprising: providing a growth substrate having a first growthsubstrate surface and a second growth substrate surface opposite to thefirst growth substrate surface, wherein the growth substrate defines aplurality of first through holes extending from the first growthsubstrate surface to the second growth substrate surface; depositing acatalyst layer on the first growth substrate surface; placing a gasdiffusing unit in a chamber comprising a first inlet and a second inletspaced apart from each other, wherein the gas diffusing unit is a hollowstructure and defines an outlet, the hollow structure has a space, andthe gas diffusing unit is used for supplying an oxygen containing gas tothe first growth substrate surface; providing a gas transporting pipehaving a first end and a second end opposite to the first end, whereinthe second end is in the chamber and connected to the gas diffusingunit, and the first end passes through the second inlet and extends outof the chamber; placing the growth substrate on the gas diffusing unitto cover the outlet, wherein the growth substrate is located between thecatalyst layer and the gas diffusing unit; supplying a carbon source gasand a protective gas to the chamber from the first inlet, and heatingthe growth substrate to a first temperature, to grow a carbon nanotubearray on the first growth substrate surface, wherein the carbon nanotubearray includes a plurality of carbon nanotubes, and each of theplurality of carbon nanotubes has a bottom end; and stopping supplyingthe carbon source gas to the chamber, supplying an oxygen containing gasto the gas transporting pipe from the first end and heating the carbonnanotube array to a second temperature, to oxidize the bottom end ofeach of the plurality of carbon nanotubes; wherein the plurality offirst through holes is used for allowing the oxygen containing gas tocontact with the bottom end.
 2. The method of claim 1, furthercomprising depositing a catalyst carrier layer on the first growthsubstrate surface before depositing the catalyst layer, and a materialof the catalyst carrier layer is selected from the group consisting ofaluminum, aluminum oxide, silicon oxide, and magnesium oxide.
 3. Themethod of claim 1, wherein a flow rate of the oxygen containing gasranges from about 300 sccm to 500 sccm, a time for oxidizing the bottomend ranges from about 5 minutes to about 20 minutes, and a pressure inthe chamber ranges from about 2 torrs to about 8 torrs.
 4. The method ofclaim 1, wherein during oxidizing the bottom end, stopping supplying thecarbon source gas from the first inlet, continuously supplying theprotective gas from the first inlet and supplying the oxygen containinggas from the first end.
 5. The method of claim 1, wherein duringoxidizing the bottom end, stopping supplying the carbon source gas andthe protective gas from the first inlet, and supplying the oxygencontaining gas and the protective gas from the first end.
 6. The methodof claim 1, further comprising separating the carbon nanotube array fromthe growth substrate after oxidizing the bottom end.
 7. The method ofclaim 6, wherein separating the carbon nanotube array from the growthsubstrate is performed by just shaking the growth substrate, justblowing on the carbon nanotube array, just tilting the growth substrate,or just turning the growth substrate.
 8. The method of claim 1, whereinthe gas diffusing unit comprises a bottom wall and a sidewall, thesidewall defines a second through hole, and the outlet is opposite tothe bottom wall.
 9. The method of claim 8, wherein the sidewall is usedto support the growth substrate.
 10. The method of claim 1, wherein ashape of the gas diffusing unit is cubic.
 11. The method of claim 1,wherein the gas diffusing unit is a semi-closed container integratedwith the gas transporting pipe.
 12. The method of claim 1, wherein thegas transporting pipe is a quartz tube, and the gas diffusing unit is aquartz boat.
 13. The method of claim 1, wherein the gas diffusing unitcomprises a first sidewall and a second sidewall opposite to the firstsidewall, each of the first sidewall and the second sidewall has a step,and the step is inside of the space.
 14. The method of claim 1, whereinthe gas diffusing unit comprises a first sidewall and a second sidewallopposite to the first sidewall, each of the first sidewall and thesecond sidewall has a plurality of steps, and the plurality of steps isinside of the space.
 15. The method of claim 1, wherein the plurality offirst through holes is used for allowing the oxygen containing gas tocontact with the bottom end.
 16. A method for making a carbon nanotubearray, the method comprising: providing a growth substrate having afirst growth substrate surface and a second growth substrate surfaceopposite to the first growth substrate surface, wherein the growthsubstrate defines a plurality of first through holes extending from thefirst growth substrate surface to the second growth substrate surface;depositing a catalyst layer on the first growth substrate surface;placing a gas diffusing unit in a chamber comprising a first inlet and asecond inlet spaced apart from each other, wherein the gas diffusingunit is a hollow structure and defines an outlet, the hollow structurehas a space, and the gas diffusing unit is used for supplying an oxygencontaining gas to the first growth substrate surface; providing a gastransporting pipe having a first end and a second end opposite to thefirst end, wherein the second end is in the chamber and connected to thegas diffusing unit, and the first end passes through the second inletand extends out of the chamber; placing the growth substrate on the gasdiffusing unit to cover the outlet, wherein the growth substrate islocated between the catalyst layer and the gas diffusing unit; supplyinga carbon source gas and a protective gas to the chamber from the firstinlet, and heating the growth substrate to a first temperature, to growa carbon nanotube array on the first growth substrate surface, whereinthe carbon nanotube array includes a plurality of carbon nanotubes, andeach of the plurality of carbon nanotubes has a bottom end; and stoppingsupplying the carbon source gas to the chamber, supplying an oxygencontaining gas to the gas transporting pipe from the first end andheating the carbon nanotube array to a second temperature, to onlyoxidize the bottom end of each of the plurality of carbon nanotubes. 17.The method of claim 16, further comprising depositing a catalyst carrierlayer on the first growth substrate surface before depositing thecatalyst layer, and a material of the catalyst carrier layer is selectedfrom the group consisting of aluminum, aluminum oxide, silicon oxide,and magnesium oxide.
 18. The method of claim 16, wherein duringoxidizing the bottom end, stopping supplying the carbon source gas fromthe first inlet, continuously supplying the protective gas from thefirst inlet and supplying the oxygen containing gas from the first end.19. The method of claim 16, wherein during oxidizing the bottom end,stopping supplying the carbon source gas and the protective gas from thefirst inlet, and supplying the oxygen containing gas and the protectivegas from the first end.
 20. The method of claim 16, further comprisingseparating the carbon nanotube array from the growth substrate afteroxidizing the bottom end, wherein separating the carbon nanotube arrayfrom the growth substrate is performed by just shaking the growthsubstrate, just blowing on the carbon nanotube array, just tilting thegrowth substrate, or just turning the growth substrate.